The invention relates to sterilization processing and particularly to the use of energetic ions for the sterilization of surfaces.
In the field of food processing, as well as in other fields, sterilization to protect against danger from harmful microorganisms is a critical concern. For the food industry, the sterilization of containers for food products is particularly important, and improvements in container sterilization processes can be expected to have a large economic impact. In the current art, sterilization of an object may be carried out by subjecting the object to heated steam pressure, to permeation by a gas such as hydrogen peroxide or ethylene oxide, and to ionizing radiation, such as a gamma-rays.
While steam-pressure sterilization can be effective, plastic packaging which will withstand the requisite temperature is more expensive than similar packaging which does not have to withstand the high-temperature. The penetration depth of high-energy electromagnetic radiation (e.g., gamma rays) is roughly six orders of magnitude greater than the size of the microorganism to be destroyed. Accordingly, high-energy radiation is effective for slow volume sterilization but inefficient for rapid surface sterilization. This inefficiency is manifested in long time scales for surface sterilization. Finally, while UV radiation has the right penetration depths for surface sterilization, sufficient intensities are difficult to achieve for providing the desired destruction rate.
Accordingly, it is an object of the invention to provide a more efficient sterilization process for food-product containers and the like. To that end, the method of the invention operates to cause a cold plasma to be disposed near a surface to be sterilized, and that cold plasma is then subjected to a pulsed voltage differential for producing energized ions in the plasma that are directed toward the surface. Those energized ions then operate to achieve spore destruction on a surface to be sterilized.
The cold plasma discharge with the parameters needed for the approach of the invention should be easily produced by a range of established techniques. The power requirements for the high voltage pulses are very modest.
A series of pulses of total duration in the range of one millisecond should be sufficient for the doses required. With pulses of this duration the charge buildup on insulating surfaces should be well within a usable range. If larger doses are required, additional pulsing can be used. The heating of the container surface is minimal for the doses required.